The present invention provides a miniaturized zoom lens system, wherein various aberrations are well compensated for over the full zoom range, and particularly, distortion. This is most difficult to compensate for in a zoom lens and is well compensated, to the same extent as in a fixed focus lens.
In a conventional two-group type zoom lens which is constructed of a first lens group (I lens group) having a negative focal length and a second lens group (II lens group) having a positive focal length, barrel distortion is markedly generated at the short focal length end. It is, therefore, difficult to obtain a miniaturized zoom lens having a small distortion to the same extent as a fixed focus lens. Hence, conventional zoom lenses have tended to be large and cumbersome.
A zoom lens having small distortion is disclosed in U.S. application Ser. No. 928,321 filed on July 26, 1978 and entitled "ZOOM LENS HAVING A SMALL DISTORTION ABERRATION". The lens disclosed therein offers a novel zoom type lens having a small distortion, which is composed of a first lens group having a negative focal length, a second lens group having a positive focal length and a third lens group having a negative focal length, the aerial spaces between the first and second lens groups and between the second and third lens groups being variable.
The above-described U.S. application Ser. No. 928,321 discloses a recognition that although barrel distortion is markedly generated between the first and second lens groups at the short focal length end, the aerial space between the second and third lens groups can be varied to be long on the short focal length side and to be short on the long focal length side. With such a technique it is relatively easy to maintain barrel distortion at a small level and at the same time spinning pin cushion distortion can also compensated to low levels.